docs: def image(self):
          """ Return string containing PNG binary image data of 2D structure image """
          if self._image is None:
              apiurl = 'http://www.chemspider.com/Search.asmx/GetCompoundThumbnail?id=%s&token=%s' % (self.csid,TOKEN)
              response = urlopen(apiurl)
              tree = ET.parse(response)
              self._image = tree.getroot().text
          return self._image